<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <!-- 使⽤正则表达式，测试⼀段字符串是否包含字⺟下划线和数字 -->
</head>
<body>
  <script type="text/javascript">
    var str = prompt('请输入字符');
    var patt=/^\w+$/;
    alert(patt.test(str));
  </script>
</body>
</html>